Optical scanning device, image display device provided with optical scanning device, retinal scanning display, and driving method of optical scanning element

Abstract

An optical scanning element performs scanning with light by bringing a mirror portion into a swinging state by generating resonance oscillations of the mirror portion due to torsional oscillations. The optical scanning element has a first resonance frequency and a second resonance frequency which generate longitudinal oscillations and lateral oscillations on a lower region side and a high region side of a resonance frequency of the torsional oscillations respectively. Outputting of a drive signal is started by setting a frequency of a drive signal which is used for oscillating the optical scanning element to a specific frequency which falls between the first resonance frequency and the second resonance frequency and is higher than the resonance frequency of the torsional oscillations and, thereafter, the frequency of the outputted drive signal is shifted to the resonance frequency of the torsional oscillations after outputting of the drive signal is started.

1. An optical scanning device comprising:
 an optical scanning element which includes a mirror portion having a reflection surface and a spring portion which is connected to the mirror portion and is configured to generate torsional oscillations which generates resonance oscillations of the mirror portion in a swinging state, the optical scanning element being configured to scan light incident on the optical scanning element due to the resonance oscillations of the mirror portion on the reflection surface, and the optical scanning element being also configured to generate subsidiary resonance oscillations consisting of longitudinal oscillations or lateral oscillations at a first resonance frequency on a lower region side and at a second resonance frequency on a higher region side with respect to a resonance frequency of the resonance oscillations in the swinging state due to the torsional oscillations; and 
 a drive signal outputting part which is configured to output a drive signal for oscillating the spring portion at a specific frequency which is a frequency between the first resonance frequency and the second resonance frequency and is higher than the resonance frequency of the torsional oscillations and, thereafter, to shift the frequency of the drive signal to the resonance frequency of the torsional oscillations. 
 
     
     
       2. An optical scanning device according to  claim 1 , wherein the optical scanning device further includes a first detection part which is configured to detect the resonance frequency of the torsional oscillations, and the drive signal outputting part is configured to adjust the specific frequency corresponding to the resonance frequency of the torsional oscillations, the first resonance frequency and the second resonance frequency. 
     
     
       3. An optical scanning device according to  claim 1 , wherein the drive signal outputting part is configured to output the drive signal with a first voltage until the oscillation frequency of the mirror portion passes the first resonance frequency lower than the resonance frequency of the torsional oscillations, and is configured to output the drive signal with a second voltage higher than the first voltage after the oscillation frequency of the mirror portion passes the first resonance frequency. 
     
     
       4. An optical scanning device according to  claim 3 , wherein the optical scanning device further includes a memory part which is configured to store preset period information as a period from a point of time that the drive signal outputting part outputs the drive signal to a point of time that the oscillation frequency of the mirror portion passes the first resonance frequency thereafter, and
 the drive signal outputting part is configured to change a voltage of the drive signal from the first voltage to the second voltage based on the period information stored in the memory part. 
 
     
     
       5. An optical scanning device according to  claim 3 , wherein an optical scanning device further includes a second detection part which is configured to detect whether or not the oscillation frequency of the mirror portion passes the first resonance frequency, and
 the drive signal outputting part is configured to change the voltage of the drive signal from the first voltage to the second voltage when the oscillation frequency of the mirror portion passes the first resonance frequency in the second detection part. 
 
     
     
       6. An optical scanning device according to  claim 1 , wherein the optical scanning element includes the mirror portion having the reflection surface which reflects light, a resilient beam which supports the mirror portion on one side thereof, a base body which supports the beam on another side of the beam, and a piezoelectric element which is mounted on at least a portion of the beam and is configured to oscillate or swing the mirror portion due to driving of the beam. 
     
     
       7. An image display device which is configured to display an image by scanning an optical flux modulated in response to an image signal on an image in two-dimensional directions by an optical scanning device, wherein
 the optical scanning device comprises: 
 an optical scanning element which includes a mirror portion having a reflection surface and a spring portion which is connected to the mirror portion and is configured to generate torsional oscillations which generates resonance oscillations of the mirror portion in a swinging state, the optical scanning element being configured to scan light incident on the optical scanning element due to the resonance oscillations of the mirror portion on the reflection surface, and the optical scanning element being also configured to generate subsidiary resonance oscillations consisting of longitudinal oscillations or lateral oscillations at a first resonance frequency on a lower region side and at a second resonance frequency on a higher region side with respect to a resonance frequency of the resonance oscillations in the swinging state due to the torsional oscillations; and 
 a drive signal outputting part which is configured to output a drive signal for oscillating the spring portion at a specific frequency which is a frequency between the first resonance frequency and the second resonance frequency and is higher than the resonance frequency of the torsional oscillations and, thereafter, to shift the frequency of the drive signal to the resonance frequency of the torsional oscillations. 
 
     
     
       8. A retinal scanning display which is configured to display an image by scanning an optical flux modulated in response to an image signal on an image in a primary direction and a secondary direction by an optical scanning device thus projecting the image on a retina of an eye provided with an optical scanning device, wherein
 the optical scanning device comprises: 
 an optical scanning element which includes a mirror portion having a reflection surface and a spring portion which is connected to the mirror portion and is configured to generate torsional oscillations which generates resonance oscillations of the mirror portion in a swinging state, the optical scanning element being configured to scan light incident on the optical scanning element due to the resonance oscillations of the mirror portion on the reflection surface, and the optical scanning element being also configured to generate subsidiary resonance oscillations consisting of longitudinal oscillations or lateral oscillations at a first resonance frequency on a lower region side and at a second resonance frequency on a higher region side with respect to a resonance frequency of the resonance oscillations in the swinging state due to the torsional oscillations; and 
 a drive signal outputting part which is configured to output a drive signal for oscillating the spring portion at a specific frequency which is a frequency between the first resonance frequency and the second resonance frequency and is higher than the resonance frequency of the torsional oscillations and, thereafter, to shift the frequency of the drive signal to the resonance frequency of the torsional oscillations. 
 
     
     
       9. A driving method of an optical scanning element, the optical scanning element including a mirror portion which has a reflection surface and a spring portion which is connected to the mirror portion and is configured to generate torsional oscillations which generates resonance oscillations of the mirror portion in a swinging state, the optical scanning element being configured to scan light incident on the optical scanning element due to the resonance oscillations of the mirror portion on the reflection surface, and the optical scanning element being also configured to generate subsidiary resonance oscillations consisting of longitudinal oscillations or lateral oscillations at a first resonance frequency on a lower region side and at a second resonance frequency on a higher region side with respect to a resonance frequency of the resonance oscillations due to the torsional oscillations, the driving method comprising the steps of:
 starting outputting of the drive signal by setting the frequency of a drive signal to a specific frequency which is a frequency between the first resonance frequency and the second resonance frequency and is higher than the resonance frequency of the torsional oscillations; and 
 shifting the frequency of the outputted drive signal to the resonance frequency of the torsional oscillations after outputting of the drive signal starts.